Transcriptome analysis and comparison reveal divergence between two invasive whitefly cryptic species

Xiao-Wei Wang,Shu-Sheng Liu,Yun-Lin Su,Jun-Bo Luan,Jun Xia,Jun-Min Li

doi:10.1186/1471-2164-12-458

Abstract

BackgroundInvasive species are valuable model systems for examining the evolutionary processes and molecular mechanisms associated with their specific characteristics by comparison with closely related species. Over the past 20 years, two species of the whitefly Bemisia tabaci species complex, Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED), have both spread from their origin Middle East/Mediterranean to many countries despite their apparent differences in many life history parameters. Previously, we have sequenced the transcriptome of MED. In this study, we sequenced the transcriptome of MEAM1 and took a comparative genomic approach to investigate the transcriptome evolution and the genetic factors underlying the differences between MEAM1 and MED.ResultsUsing Illumina sequencing technology, we generated 17 million sequencing reads for MEAM1. These reads were assembled into 57,741 unique sequences and 15,922 sequences were annotated with an E-value above 10-5. Compared with the MED transcriptome, we identified 3,585 pairs of high quality orthologous genes and inferred their sequence divergences. The average differences in coding, 5' untranslated and 3' untranslated region were 0.83%, 1.66% and 1.43%, respectively. The level of sequence divergence provides additional support to the proposition that MEAM1 and MED are two species. Based on the ratio of nonsynonymous and synonymous substitutions, we identified 24 sequences that have evolved in response to positive selection. Many of those genes are predicted to be involved in metabolism and insecticide resistance which might contribute to the divergence of the two whitefly species.ConclusionsOur data present a comprehensive sequence comparison between the two invasive whitefly species. This study will provide a road map for future investigations on the molecular mechanisms underlying their biological differences.

Highlights

Invasive species are valuable model systems for examining the evolutionary processes and molecular mechanisms associated with their specific characteristics by comparison with closely related species
Illumina sequencing and reads assembly of Middle East-Asia Minor 1 (MEAM1) transcriptome To obtain an overview of the MEAM1 whitefly transcriptome, a cDNA sample was prepared from a mixture of RNA from egg & nymph, pupa, female adult and male adult at equal ratio, and sequenced using the Illumina sequencing platform
We obtained a total of 17 million of 75 bp reads, which have been deposited in the NCBI Short Read Archive (SRA) under the accession

Summary

Introduction

Invasive species are valuable model systems for examining the evolutionary processes and molecular mechanisms associated with their specific characteristics by comparison with closely related species. Genomic resources and information about invasive species are valuable for evolutionary studies to determine how and why phenotypes specific to non-indigenous species have been formed [1,2]. They will aid ongoing efforts to understand and control the ecological, genetic and economic impacts of the invasive species. Asymmetric mating interactions between MEAM1 and its indigenous competitors have been shown to play a major role in the invasion of MEAM1 into China and Australia [19] While both MEAM1 and MED are known for their invasiveness, their biological characteristics are rather different. In 2005, MED appeared and gradually replaced MEAM1 and has become the only or predominant B. tabaci in some locations [37]

Methods

Results

Discussion

Conclusion